Photoreceptors transform light energy impinging on the retina into neural signals, and lateral interactions between the receptors probably code many attributes of visual stimuli. Information not integrated into the neural code is lost to the organism. Hence, knowledge of distal retinal processes not only provides information about these neural elements, but also is a necessary prerequisite to understanding more central mechanisms in the visual system. Intraretinal microelectrode recording techniques provide access to the slow extracellular signals generated by the neurons in the distal retina. By appropriate stimulus manipulation individual extracellular potentials may be studied. Temporal and color vision questions are of foremost interest, since distal retinal processes probably limit many aspects of the visual system's response in these domains. By using cynomolgus macaque monkeys, which have human-like visual systems, we can address questions pertinent to human visual perception. In conjunction with extracellular studies, we propose to record intracellularly, in vivo, from cells in the distal retina of monkey in order to better define the source of the extracellular potentials and clarify the neural networks underlying them. An important spin-off of the proposed research is the eventual study of retinal processes in man, including diagnosis of disease entities. Identification of psychophysical phenomena determined in the distal retina would provide a means of better defining retinal disease processes in man via psychophysical tests. Quantitative analysis of retinal potentials and positive identification of their source will enhance the electroretinogram as a diagnostic tool.